Note: Descriptions are shown in the official language in which they were submitted.
2.29319
Patent Application
Attorney's Docket No. D/93479
MAGNETIC BRUSH DEVELOPMENT APPARATUS FOR TONER
ADD/MIX DISPENSER
BACKGROUND OF THE INVENTION
The present invention relates to electrostatographic printing
apparatus and in particular to an automatic toner dispensing apparatus for
use with two component development apparatus.
In the process of electrostatographic printing, a
photoconductive surface is charged to a substantially uniform potential.
The photoconductive surface is imagewise exposed to record an
electrostatic latent image corresponding to the informational areas of an
original document being reproduced. This records an electrostatic latent
image on the photoconductive surface corresponding to the informational
areas contained within the original document. Thereafter, a developer
material is transported into contact with the electrostatic latent image.
Toner particles are attracted from the carrier granules of the developer
material onto the latent image. The resultant toner powder image is then
transferred from the photoconductive surface to a sheet of support
material such as paper and permanently affixed thereto.
This process is well known and useful for light lens copying from
an original and in printing applications from electronically generated or
stored originals.
Figure 1 is representative of a common configuration in
electrostatographic printing apparatus wherein a two component
magnetic brush development apparatus comprising a rotatable developer
roll 10 rotating about fixed magnets 11 in the direction indicated by the
arrow creating a magnetic field to attract two component developer to the
surface of the developer roll is trimmed by a trim bar 12 to provide a
-1-
2129318
uniform thickness of developer on the developer roll 10 to present this
layer of developer to the surface of the photoreceptor 13 Which has an
electrostatic latent image on it's surface to attract the toner material from
the developer roll surface to the surface of the photoreceptor m image
configuration which is subsequently transferred electrostatically by transfer
corotron 14 to a substrate 15 such as ordinary paper which is then detacked
from the surface of the photoreceptor by detack corotron 18 and
transported to the fuser (not shown) for fixing to the substrate. Any toner
remaining on the surface of the photoreceptor is cleaned therefrom by a
cleaner blade 19 and transported to a cleaner sump (not shown) by an
auger 20. The developer, which comprises carrier particles such as steel shot
and very much smaller thermoplastic resin toner particles is housed in the
developer sump 21 with a paddle wheel 22 to mix the developer and
present it to the developer roil to continually provide a supply of developer
to the magnetic brush development roll 10. For additional details of this
process, attention is directed to U.S. Patent No. 2,874,063 and for further
information about the process, in general, attention is directed to the book
Electrophotography by R. M. Schaffert, Enlarged and Revised Edition; 1975
published in the U. S. by Halsted Press, a division of John Wiley & Sons, New
York. In this process,
the individual toner particles are charged and attracted to the image on the
photoreceptor thereby depleting the total developer supply ~n the
developer sump of toner particles. Accordingly, it is necessary to replenish
the toner in the developer to maintain a sufficiently high concentration of
toner to ensure satisfactory image density in the final print. One previous
approach to doing this is illustrated in Figure 1 and also Figure 4, wherein
freshly supplied toner is supplied to one end of a toner dispensing tube 24
from a toner hopper 23. As previously discussed, the level of developer on a
developer roll is controlled by a trim bar 12, which directs the excess
developer back to the developer sump. As illustrated in Figures 1 and 4,
while a majority of the developer trimmed by the trim bar flows to a baffle
25 with the majority falling back into the paddle wheel sump 21, the baffle
25 has a feature, such as a bridge 28 that allows a small amount of
_2_
A
a~n
F129319
developer to be fed into the dispense tube 24 through an opening 27 at the end
of the dispense
tube where freshly supplied toner is introduced from the toner hopper. The
dispense tube has
an auger 29 in the tube which mixes the new toner with the feedback developer
in the tube
from the bridge 28. This facilitates the handling of toner since developer
flows much more
readily than toner. Physically, the carrier in the developer is about ten
times the size of the
toner particles, is much greater in mass and density, has additional different
material
characteristics which enable the feeding of a much larger volume of developer
because of the
feedback of a portion of the excess developer than of the toner alone. In this
particular
machine configuration the requirements for replenishing toner are so small
that the toner only
flow rate along the length of the tube would be very low and it would be very
difficult to
handle the small amounts of toner because of tolerances and clearances between
the auger
and the tube, Accordingly, the feedback flow of developer to the dispensing
tube enables a
more efficient transport of newly supplied toner and developer down the tube
since the ratio
of the carrier to toner is from 50 to 100 to one by mass. From the dispense
tube the toner
enriched developer is supplied to a mixing chamber 31 which has a wobble plate
mixer 32
and is augered from one end of the dispensing tube down to the other end of
the dispensing
tube. The toner enriched developer is supplied to the mixing chamber through a
slot 33 (see
Figure 2) in the bottom of the tube which gets increasingly wider down the
length of the slot
from the toner and developer input end to the opposite end of the dispensing
tube. The
wobble plate cross mixing device 32 is well known and comprises a rotary
device with
elliptical plates off axis to mix the toner and developer as the toner is
dispensed through the
mix in the mixing chamber 31. A dividing plate 35 is provided to limit the
area in which
mixed developer can flow to the development chamber 36.
While capable of performing satisfactorily under certain conditions it has
been
discovered that the feedback flow rate of developer from the developer roll
trim bar to the
dispensing tube will vary depending on the strength of the magnetic roll and
the pick up of
developer from the surface of the developer roll which varies from machine to
machine due
to differences in manufacturing tolerances. This variation in feedback flow
rate into the
-3-
y,;,
/::,..'
~1~g31g
dispensing tube causes variations in the dispensing uniformity out of the tube
and into the
mix chamber with the slotted tube configuration as may be observed with
reference to Figure
3, which illustrates this distribution of developer and toner over the width
of the dispense
tube at four different feedback flow rates. For high flow rate there is
initially a very high
dispensing intensity and at low flow rates there is essentially none. This
nonuniform
distribution results in poor developer uniformity in the mixing chamber and
the developer
housing resulting in uneven development uniformity and poor print quality.
SUMMARY OF THE INVENTION
In accordance with a principle aspect of the present invention; a developer
dispensing
assembly and two component development apparatus having the developer
dispensing
assembly is provided with a novel developer dispensing assembly is provided
with a novel
developer dispensing tube having an array of developer dispensing apertures
arranged in a
geometric pattern having a spatial relationship with respect to each other to
dispense freshly
toner enriched developer material through the apertures to the development
apparatus at a
substantially uniform dispensing profile as the toner enriched developer is
transported from
the first end of the dispense tube to the opposite end of the dispense tube
for varied feed rates
of developer and tone to the dispensing tube wherein the geometric pattern of
the apertures
comprises a primary group of in line apertures having a spatial frequency
between adjacent
apertures which is less at the first end of the tube that an the opposite end
of the tube; and
wherein said geometric pattern includes at least one secondary group of in
line apertures
spaced above the primary group of in line apertures.
In a further aspect of the present invention, the dispensing tube is
substantially circular
in cross section and has an auger to transport developer and toner from the
first end to the
opposite end of the tube.
In a further aspect of the present invention, the apertures in the developer
dispensing
tube are circular.
In the further aspect of the present invention, a toner hopper supplies a
fresh supply of
toner and the developer supply is a feedback of a portion of developer from
the development
-4-
c
F92g319
apparatus. The developer dispensing apertures are at the bottom of the tube
and parallel to
the tube axis so that developer and toner flow by gravity through the
apertures to the
development apparatus.
In the further aspect of the present invention, the geometric pattern of
apertures
comprises a primary group of in line apertures having a spatial frequency
between adjacent
apertures which is less at the first end of the dispensing tube than at the
opposite end of the
dispensing tube.
In a further aspect of the present invention, the primary group of in line
apertures are
arranged in a plurality of sets of at least two apertures with the apertures
of each set having a
spatial frequency substantially the same and the apertures in successive sets
from said first
end to said opposite end being of increased spatial frequency with respect to
the immediately
preceding adjacent set.
In a further aspect of the present invention, the geometric pattern includes
at least one
secondary group of in line apertures spaced above the primary group of in line
apertures.
In a further aspect of the present invention, a secondary group of in line
apertures
extends substantially from the first end of the tube to about the midpoint of
the tube and
includes at least one aperture at the end of the primary group of in line
apertures.
In a further aspect of the present invention, the dispensing assembly includes
a
developer bail out gate at the opposite end of the tube and includes an
opening in the tube at
the first end to receive developer from the development apparatus.
Yet another aspect of this invention is as follows:
Two component magnetic brush development apparatus including means to deliver
two component developer to a developer roll rotatable about at least one
stationary magnet, a
trim bar to control the level of developer on said rotatable developer roll,
means to enable a
portion of developer trimmed by said trim bar to be delivered to a developer
dispensing
assembly for initial contact with freshly dispensed toner, means to mix
developer with
freshly dispensed toner, said developer dispensing assembly comprising a
developer
dispensing tube, a toner supply means at a first end of said tube, developer
supply means
adjacent said toner supply means, transport means to transport toner and
developer from said
-5-
~12g319
first end of said tube to the opposite end of said tube, said developer
dispensing tube having
an array of developer dispensing apertures arranged in a geometric pattern
having a spatial
relationship with respect to each other to dispense developer and toner
through said apertures
to said development apparatus at a substantially uniform dispensing profile as
said developer
and toner are transported from said first end of said tube to said opposite
end of said tube for
varied feed rates of developer and toner to said dispensing tube;
wherein said geometric pattern of said apertures comprises a primary group of
in line
apertures having a spatial frequency between adjacent apertures which is less
at the first end
of said tube than at the opposite end of said tube; and
wherein said geometric pattern includes at least one secondary group of in
line
apertures spaced above the primary group of in line apertures.
For a better understanding of the invention as well as other objects and
further features
thereof reference is had to the following drawings and descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation in cross section illustrating a typical
electrostatographic printing apparatus which may employ the developer
dispensing assembly
according to the present invention.
- Sa -
~12931~
Figure 2 is a bottom view illustrating the slotted tube
configuration according to prior art practice.
Figure 3 is a graphical representation of the dispensing profile to
the mixing chamtJer for the slotted configuration of Figure 2 for various
feedback flow rates to the dispensing tube.
Figure 4 is an isometric representation of the developer roll,
developer trim bar, baffle, bridge to the dispensing tube for developer and
the toner hopper at the first end of the dispensing assembly.
Figure S is an isometric view of the dispensing tube according to
the present invention with the apertures arranged in a geometric pattern.
Figure 6 illustrates the dispense profile of a dispensing tube
having one level hole configuration with the apertures being evenly
spaced.
Figure 7 is an illustration of a dispensing profile having
progressively spaced apertures in a two level aperture configuration as
illustrated in Figure 5. The dispense profiles in Figures 6 and 7 are for
feedback flow rates of 2.5 grams/second.
Figure 8 illustrates the dispense profile of toner enriched
developer to the mixing chamber for various feedback flow rates to the
dispensing tube.
Figures 9A and 9B illustrate the two row design compensating
for varying flow rates and pile heights.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention will now be described by reference to a preferred
embodiment.
For ease of construction and explanation the invention will be
described with reference to the apparatus illustrated and previously
described in Figures 1 and 4 with the exception of the developer dispensing
to be.
The developer dispensing assembly according to the present
invention has a dispensing tube with an array 40 of developer dispensing
apertures 41 arranged in a geometric pattern (see Figures 5 and 7) to
-6-
X929319
dispense toner enriched developer therethrough to the development
apparatus at a substantially uniform dispensing profile along the length of
the tube for varied feed rates of developer and toner according to the
following considerations. 3oth toner and developer material are
introduced into a first end of the dispensing tube 24. The toner enriched
development material is then transported down the tube by an auger 29.
The developer material forms piles within the tube of a certain size and
mass at the driving side of each auger pitch, depending on the flow rate
into the tube, the tube and auger geometry, the auger speed and the flow
characteristics of the developer material. These piles are driven and
propagate through the tube toward the opposite end of the tube. The
tube has an in line series of apertures or holes in it of equal size and as a
pile
of developer material passes over a hole, a percentage of the original mass
of the pile is dispensed out of the aperture or hole thereby reducing the
pile size and mass for the next hole it is to encounter. As the pile size
diminishes the pile dwell time over successive holes is lessened thereby
reducing the mass dispensed out of downstream holes relative to upstream
holes. As a result of this continual incremental reduction of dispense rate
per hole the whole spatial frequency is continually increased to gain an
aggregate uniform dispense profile. The hole size, number of holes and
varying spatial frequency are selected for the system geometry, auger
speed and minimum flow rate of material entering the dispensing tube. If
the hole size is too large and the initial spatial frequency too tight, the
vast
majority of material is dispensed toward the upstream end of the tube
yielding an upstream skewed dispense profile.
The mass flow rate of toner and developer material into the
tube may vary due to factors external to the dispensing tube which means
that the dispensing tube needs to tolerate a range of flow rates and still
deliver a substantially uniform dispensing profile along the length of the
tube. As the input flow rate increases, the pile size and dwell time of the
pile of each auger pitch continues to increase, as would the dispense duty
cycle of a hole it passes over eventually overlapping with an adjacent auger
pitch pile at which point a threshold or maximum 100 percent duty cycle
_7_
- 2129319
hole dispense rate is reached. This saturation of hole dispense rate occurs
first at the furthest upstream hole. As the flow rate continues to increase,
more and more holes saturate going from upstream to downstream.
During this increase in flow rate an increasing mass of material is augered
toward the downstream end of the tube, any remaining toner enriched
developer present at the end of the tube is dispensed out of a large bail out
gate hole 43 (see Figure 7). Once all of the holes reach saturation, the bail
out gate hole flow rate continues to increase yielding a dispense profile
spike at the downstream end of the tube.
To accommodate such high flow rate conditions at least one
secondary group of in line equal size holes may be placed at some position
above the primary in line group. These holes serve to uniformly distribute
material that would have otherwise been pumped out the bail out gate
hole. The number of holes and spatial frequency is selected for the process
taking into consideration their interaction with an effect on the primary
group of holes. These holes in the secondary group only become active
under high flow rate conditions when the pile size height is large or high
enough to reach that point on the dispense tube wall. As may be observed
with reference to, in particular, Figures 5, 9A and 9B, the primary role of
apertures while at the bottom of the tube is slightly offset to one side and
therefore slightly up the side of the tube to both enable the toner enriched
developer to be directed to the cross mixer and to ensure that there is some
mixing of developer and newly applied toner. The secondary role of
apertures is even further up the side of the tube and in some areas along
the length of the tube where there is a low pile height does not dispense
the toner enriched developer.
On the above considerations an array 40 of developer dispensing
apertures in the dispensing tube 24 arranged is in a geometric pattern
having a spatial relationship with respect to each other to dispense toner
enriched developer through the apertures to the development apparatus
at a substantially uniform dispensing profile for a variety of feedback rates
of developer and toner to the dispensing tube. The array 40 of dispensing
apertures 41 are circular and of the same general cross sectional area and
_g_
X129319
are arranged in a line parallel to the axis of the dispensing tube which is
also circular and contained therewith in a rotatable auger. The apertures
are arranged at the bottom of the tube so that the developer and toner fall
by gravity through the apertures to the development apparatus. The
geometric pattern of the apertures includes a primary group 45 of in line
apertures having a spatial frequency between adjacent apertures lesser
than at the first end 46 of the dispensing tube 24 than at the opposite end
of the dispensing tube and preferably has the apertures arranged in a
plurality of sets of at least two apertures with the apertures of each set
having a spatial frequency substantially the same in the apertures in
successive sets from the first end to the opposite end of the dispensing tube
and being of greater spatial frequency with respect to the immediately
preceding adjacent set. (See Figures 5 and 7). As previously indicated to
accommodate high flow rate conditions there is at least one secondary
group 48 of in line apertures spaced above the primary group 45 of in line
apertures in a line parallel to the axis of the dispensing tube. While only
one secondary group of in line apertures is illustrated in Figures 5 and 7, it
will be understood that for even higher flow rates of developer an
additional line or two of apertures may be provided. However, as indicated
in Figure 7, the secondary group of in line apertures extend substantially
from the first end of the tube 46 to about the midpoint of the tube and
includes at least one aperture 48 at the end of the primary group 45 of in
line apertures.
The developer dispense profile of this progressively spaced two
level hole configuration is illustrated in Figure 7 as is the bail out gate
previously discussed. Figure 6 is presented for comparative purposes to
illustrate the aperture hole spacing and dispense profile for a dispensing
tube have evenly spaced one level hole configuration. Figure 8 illustrates
the substantially uniform dispensing rate of developer and toner along the
length of the dispense tube of Figures 5 and 7. Figure 9 illustrates the total
dwell time of varying pile heights over the dispensing hole. Thus, for a pile
height such as that simulated in Section A of Figure 9A toner enriched
developer is dispensed from all the primary group of in line holes covered
_g_
2'128319
by the pile and also all the secondary group of in line holes in this section.
However, as the pile height decreases due to depletion of toner enriched
developer and its natural width for that height decrease the dispense duty
cycle of downstream holes ~s gradually reduced initially from the secondary
group of in line holes to a point where they no longer are dispensing toner
enriched developer due to the apex of the pile being below them as
illustrated in Section B. This reduction in dispense rate ~s compensated by
increasing the spatial frequency of the primary group of in line holes to
provide the desired substantially uniform dispense profile for varied
developer feedback flow rates. The vertical position of any hole from a
base of a pile will influence the dwell time of the pile over that hole since
the work of a pile decreases from the maximum at the base of the pile to 0
at or just above the apex of the pile. In turn, the hole dispense duty cycle,
the total hole flow rate per pile interaction on subsequent downstream
holes and ultimate dispense profiles are effected.
Thus, according to the present invention a developer dispensing
assembly has been provided which has a developer dispensing tube having
an array of developer dispensing apertures arranged in a geometric pattern
having a spatial relationship to dispense developer and toner as toner
enriched developer to a development apparatus at a substantially uniform
dispensing profile for a variety of feed rates of developer and toner. This
enables a wider latitude in flow rate of the developer to the dispensing
tube which may depend on magnetic field strength considerations as well
as making it more tolerant to variations in process parameters.
Thus, according to the present invention a printing apparatus
with deferred jam clearance is provided. Furthermore, while the invention
has been described with regard to electrostatographic printing apparatus,
it will be understood that it has equal application to other types of printing
and sheet handling devices. Furthermore, while the invention has been
described with reference to a copier it has equal application to other
-10-
E
~12931g
machines such as printers where the image is electronically generated.
Accordingly, it is intended to embrace all such alternatives and
modifications as may fall within the spirit and scope of the appending
claims.
-11-
